This invention relates to an electrostatic precipitator for the cleaning of air.
Electrostatic precipitators for air cleaning are based on the principle that particles, which to a large extent are not charged, upon entering the precipitator are charged in a first stage when passing between two electric conductors, such as a wire and two metal sheets positioned one on each side of the wire, where the sheets and the wire have different electric potentials. A particle thus charged is thereafter separated from the air stream, for example, the air stream with a charged particle passes between two metal sheets with different electric potentials whereupon the charged particle is attracted to one of the sheets which has a polarity opposite to that of the particle.
The efficiency of an electrostatic precipitator depends to a very high degree on the dimensioning of the charging stage in relation to the separation stage. Attempts have heretofore been made to increase the capacity of the electrostatic precipitator by increasing the field strength at the charging and separation stage and by extending the separation stage. These measures increase the capacity of a precipitator, but only to a certain level, because on one hand the field strength cannot be increased indefinitely and on the other hand the separation stage must be increased substantially, if a decisive difference in efficiency is to be obtained.
A great disadvantage arising in connection with an increase of the potential in the charging stage is the increase in ozone production.
Electrostatic precipitators at present commercially available separate 50-60% of the particles entering the precipitator. The electrostatic precipitator according to the present invention separates up to 97% of the entering particles.
The present invention relates to an electrostatic precipitator for air cleaning which comprises a charging portion, a separation portion and a potential supply means, said charging portion including wires, which are positioned between parallel grounded metal sheets and have an electric potential other than that of the metal sheets, and said separation portion including additional parallel metal sheets, each of which has an electric potential other than that of adjacent metal sheets (as will be hereinafter described), and said charging portion including two or more wires between each pair of metal sheets.
The invention is characterized thereby that the relative distance C between two or more wires located between two of said parallel metal sheets lies within the interval described by the formula C=(V.multidot.T)/(n-k) where k.epsilon.{0,n-2} and V is the particle speed, T is the cycle time for a varying direct potential generated by the potential supply means, and n is the number of wires, and that the distance C preferably is chosen within the interval 0.6.multidot.b.ltoreq.C.ltoreq.1.2.multidot.V.multidot.T/2 where b is the distance between each wire and the surrounding metal sheets .